Reverse osmosis is very good at its job. Its membrane blocks anything larger than a water molecule, which is why it removes heavy metals, dissolved salts and most contaminants so effectively. But that membrane cannot distinguish between what you want gone and what you would rather keep. Calcium, magnesium and potassium are dissolved minerals too, and they leave with everything else.

The result is water that is genuinely clean and almost entirely empty. Remineralisation is the step that puts the minerals back.

What remineralisation actually means

Remineralising water means adding dissolved minerals back into it after purification, so the water you drink resembles natural spring water rather than distilled water. It is not about making water "healthier" than nature intended. It is about restoring what the purification process took out.

Natural groundwater and spring water pick up minerals as they move through rock. That is where the taste of good water comes from, and why bottled mineral water lists a mineral composition on the label. RO water has none of that, because the membrane removed it.

Why RO removes minerals in the first place

An RO membrane has pores around 0.0001 microns across. Dissolved mineral ions are comfortably larger than a water molecule, so they are rejected along with contaminants and flushed away in the reject stream.

This is inherent to how the technology works, not a fault in your purifier. A membrane that let calcium through would let other dissolved solids through as well. The trade-off is the point of the design.

Three ways to remineralise RO water

1. Mineral cartridges fitted to the purifier

An inline cartridge sits after the membrane and releases minerals as water passes. It is automatic, but it is also a consumable with a fixed life, the mineral release rate falls as it depletes, and you have limited control over dosage.

2. Alkaline filters

These raise the pH of water, and often add some minerals as a side effect. Their primary purpose is pH rather than mineral content, so the two aims are easy to confuse.

3. Concentrated mineral drops

A liquid mineral concentrate added directly to the glass or bottle. You control the dose, the purifier needs no modification, and it works with any water source — including water you did not purify yourself.

This is the approach M-Shot takes: a concentrated mineral liquid complex, added a few drops at a time.

Which minerals matter

The minerals commonly removed by RO and worth restoring are magnesium, calcium and potassium, along with trace minerals present in much smaller amounts. These contribute to the taste and mineral balance of drinking water.

Form matters as much as presence. Minerals in ionic form are already dissolved and dissociated in water, which is how minerals occur in natural spring water — as opposed to powdered rock minerals, which must first be broken down.

Do you need to remineralise?

If RO is your only source of drinking water, it is worth considering. Most people get the bulk of their minerals from food, and water is a smaller contributor. But water is something you drink several litres of every day, and the taste difference alone is noticeable to most people.

If your water comes from a mixed supply, or you drink a lot of mineral water already, the case is weaker. It is a reasonable thing to decide for yourself rather than be sold on.